Final answer:
The glossopharyngeal nerve (CN IX) functions in taste sensation for the posterior tongue.
Step-by-step explanation:
The function of the glossopharyngeal nerve (CN IX) is taste sensation for the posterior tongue. The glossopharyngeal nerve connects to taste buds in the posterior two thirds of the tongue. Along with taste, the glossopharyngeal nerve also relays general sensations from the pharyngeal walls and can stimulate the gag reflex. It does not control facial muscles, hearing and balance, or smell perception.